The useful range of a driver is greatly affected by the drive power requirements of the load and the thermal characteristics of the IC package. For a power driver to be useful over a particular temperature range, the package must allow for the efficient removal of the heat produced while keeping the junction temperature within rated limits. The UCC2742x-Q1 family of drivers is available in three different packages to cover a range of application requirements.

As shown in the power dissipation rating table, the 8-pin SOIC (D) package has a power rating of around 0.5 W with T_A = 70°C. This limit is imposed in conjunction with the power derating factor also given in the Section 6.7 table. Note that the power dissipation in our earlier example is 0.432 W with a 10-nF load, 12 V_DD, switched at 300 kHz. Thus, only one load of this size could be driven using the D package, even if the two onboard drivers are paralleled. The difficulties with heat removal limit the drive available in the older packages.

The 8-pin MSOP with PowerPAD (DGN) package significantly relieves this concern by offering an effective means of removing the heat from the semiconductor junction. As described in reference 2 of the Section 11.2.1, the PowerPAD packages offer a leadframe die pad that is exposed at the base of the package. This pad is soldered to the copper on the PCB directly underneath the IC package, reducing the R_θJC(bot) down to 5.9°C/W. Data is presented in reference 2 of Section 11.2.1 to show that the power dissipation can be quadrupled in the PowerPAD configuration when compared to the standard packages. The PCB must be designed with thermal lands and thermal vias to complete the heat removal subsystem. This allows a significant improvement in heat sinking over that available in the D package, and is shown to more than double the power capability of the D package. Note that the PowerPAD is not directly connected to any leads of the package. However, it is electrically and thermally connected to the substrate which is the ground of the device.